This invention relates to an apparatus for subjecting fluids to ultraviolet (UV) light. The apparatus may be used for water sterilization and is intended for Point-of-Entry use. More particularly it relates to an apparatus for use in water purification having improved effectiveness through the employment of a self-cleaning mechanism to maintain a desired degree of transmittance of ultraviolet radiation through an ultraviolet transparent quartz tube for ultraviolet lamps. The apparatus includes an efficient arrangement of light shielding baffles to protect UV sensitive components from the UV light. The apparatus is provided as a component in a housing having a modular design.
Point-of-Entry ultraviolet water sterilization devices typically include a pressure vessel including a stainless steel cylinder enclosing a smaller concentric quartz light transmission tube. Within the quartz tube is a tubular discharge lamp emitting light with wavelengths typically centered around 254 nm, which is referred to as ultraviolet light or ultraviolet radiation. Ultraviolet (UV) light represents a section of the overall electromagnetic spectrum of light, extending from the blue end of the visible at about 400 nm to a region of about 100 nm.
Water to be exposed to the light from the lamp is passed between the interior surface of the steel cylinder and the exterior surface of the light transmission tube. One important limitation to this type of device is that the exterior surface of the quartz tube becomes fouled with inactivated biological contaminants in the water as well as minerals at least in part due to a photochemical reaction upon exposure to the light of the lamp. Due to the arrangement of the discharge lamp contained in a quartz sheath, the foulants collect on the exterior of the quartz tube. The foulants cause a reduced transmission of ultraviolet light through the light transmission tube, which results in a reduced efficacy of the device. This requires that the device be disassembled periodically for cleaning of the quartz tube to maintain its effectiveness.
To reduce maintenance and downtime, automatic wiping mechanisms have been tried on these systems with limited success. U.S. Pat. No. 5,266,280 discloses a system of radially mounted brushes that act to wipe the external surface of the quartz sheath. This costly mechanism is difficult to actuate and to provide adequate sealing for the power transmission shaft connected to the motor outside of the steel cylinder of the pressure vessel. Also described are a number of other similar external wipers, which have varying amounts of effectiveness. Cleaning the tube in this manner is cumbersome and compromises the irradiation dosage of the device because the gap between the outer wall of the quartz sheaf and the inner wall of the pressure vessel must be increased to accommodate the wiper resulting in a larger dosage gradient across the laminar fluid cross section.
Attempts have been made at providing means to conduct fluid through a quartz tube with UV emitting lamps arranged external to the quartz tube and with a wiper mechanism acting to clean the inside walls of the tube. These attempts have failed primarily due to material degradation. The ultraviolet light emitted by germicidal lamps causes degradation of some form in all polymer-based materials. Many components used in the construction of an internal automated wiper system must be polymer-based for friction reduction, manufacturability and sealing-performance reasons. U.S. Pat. No. 5,266,280 describes a number of UV resistant materials such as halogenated polyolefins, urethane, synthetic rubber and high-density polypropylene, all of which are susceptible to being degraded by UV light. Some polymeric materials exist which resist UV degradation. However, when they are exposed to UV radiation centered around 254 nm, and are provided in contact with the fluid being sterilized, will leach small doses of volatile organic compounds. This defeats the purpose of purification. Materials certified by government organizations for use with potable water are tested without irradiation of UV light and many polymers in this category are found to be non-compliant after irradiation. For this reason it is unacceptable to simply claim compliance for potable water of materials used in irradiated locations of UV sterilization devices as is typically done.
U.S. Pat. No. 4,002,918 discloses a device of similar arrangement for the purpose of xe2x80x9cthe irradiation of fluids to initiate chemical reactionsxe2x80x9d, but describes wiper materials as being plastic, which are unacceptable for ultraviolet water sterilization applications. There is no mention of shielding materials from harmful ultraviolet light to prevent the leaching of volatile organic compounds, which has been observed to be a critical factor in the design of ultraviolet water sterilization devices.
There is a demand for a UV water purification device that combines superior performance and low maintenance costs. The present invention satisfies the demand.
A preferred embodiment of the invention is illustrated with respect to an ultraviolet water purification device or reactor with a novel arrangement of components and materials that provides superior performance and serviceability and yet still allows manufacturability at reasonable cost and by relatively simple means.
According to an aspect of the invention, an apparatus that employs plates formed of a material impervious to ultraviolet radiation on all wavelengths, which acts to shield other components such as rubber and polymer-based seals and bearings from the harmful effects of direct ultraviolet irradiation.
The apparatus includes a tubular body, which may be a quartz tube for conducting fluid therethrough having an internally mounted wiper for the continuous cleaning of an inside surface of the tubular body. Potentially biologically contaminated fluids are irradiated by at least one radiation source including at least one elongated discharge lamp mounted externally with respect to the fluid-conducting tubular body. The wiper is formed of stainless steel or other UV-impervious materials. The wiper may include a rectangular elongate blade mounted to a shaft extending along the long axis of the apparatus. The blade may be provided with one or more holes for increased light penetration and for the production of turbulence. The blade may include slits formed therein, for stress relief of the blade, which extend perpendicular to the axis of the shaft. The radiation source may be surrounded with high-efficiency reflectors designed to concentrate light on the central axis of the fluid being conducted through the tubular body.
One embodiment of the apparatus of the present invention provides irradiation of a fluid with UV light and includes a tubular body consisting of a UV-permeable material. The tubular body includes an inner surface defining a fluid chamber and open first and second ends for ingress and egress of the fluid through the fluid chamber. At least one UV radiation source is provided and is so arranged relative to the tubular body as to subject the chamber to the UV light. A wiper is centrally supported in said body for rotation therein, sized and shaped to contact the inner surface. First and second light baffles are positioned inside the tubular body adjacent respective first and second ends and define an irradiated section of the fluid chamber therebetween to prevent UV light penetration beyond the irradiated section of the fluid chamber while permitting the fluid to flow through the apparatus.
The apparatus is provided as a component in a housing having a modular design. One aspect of the invention provides an apparatus for irradiation of a fluid with UV light including a back cover for mounting on a surface. A tubular body is mounted to the back cover. The tubular body includes an inlet and an outlet for ingress and egress of the fluid through the tubular body. One of the inlet and the outlet includes a valve. An inner cover is attached to the back cover. One or more radiation source is attached to the inner cover. The one or more radiation source produces UV light so arranged relative to the tubular body as to subject the fluid to the UV light. An electronics module is attached to the inner cover and is electrically connected to the valve and the one or more radiation source for controlling operation thereof. A front cover is attached to one of the inner cover and the back cover.
These and other advantages, as well as the invention itself, will become apparent in the details of construction and operation as more fully described and claimed below. Moreover, it should be appreciated that several aspects of the invention can be used in other applications where irradiation of fluids would be desirable.